The present invention relates to a radio receiver and, more particularly, to a radio receiver receiving both a voice and a data signal.
If a radio receiver receives a radio signal having a relatively low level, the receiver produces a demodulated baseband signal with an impaired signal-to-noise (S/N) ratio. To improve the S/N ratio, several ways may be employed. An example for a satellite broadcasting receiver is disclosed in Japanese Patent Application Publication (Kokai) 63-39291 (39291/1988). The disclosed broadcasting receiver includes a frequency-modulation (FM) demodulator having a phase-locked loop (PLL) circuit and a receiving condition decision circuit. In response to the output of the receiving condition decision circuit, a controller controls the bandwidth of a loop filter within the PLL circuit to obtain an optimized video signal.
Since the broadcasting receiver includes the PLL circuit, it is difficult to broaden the receiving bandwidth which is restricted by the response characteristics of the PLL circuit. Also, the PLL circuit inherently has a problem of out-of lock. Since linear amplification is required prior to the PLL circuit to improve the S/N ratio, the broadcasting receiver is not suitable for a mobile communications system in which an input to a demodulator, namely, a frequency discriminator must be amplitude limited to depress amplitude fluctuations in the received signal.